Method of and apparatus for testing ignition



Jan. 11 1949. w. M. BAUER 2,458,974

HETHOD OF AND APPARATUS FOR TESTING IGNITIONS llllll Ivv" - 4o J ,3 I

Fial: .7 5= 37 I a 35 5 7? 4 INVENTOR.

WILLIAM MALCOLM BAUER ATTORNEY PatentedJan. ll, 1949 Mlrrnon or AND arrana'rus ron 'rasrmc ram-non William Malcolm Bauer, Glen 'Ridge, N. 1.. aselgnor to Curtis-Wright Corporation, Bloomfleld, N. J., a corporation of Delaware Application June 2, 1945, Serial No. 591,224

16 Claims. (Cl. 175-183) This inventionrelates to ignition testing, and particularly to the testing of spark plugs in dualignition internal combustion engines, such as aircraft motors, for example.

The servicing of ignition systems of aircraft motors has heretofore consumed a large part of the time required for ground maintenance of large transport and military aircraft. A frequent source of trouble is faulty or fouled spark plugs. In such cases, the conventional method is to remove all plugs from the engine and to replace them with new ones. In the case of an eighteen cylinder motor. for example, this procedure requires approximately twelve man-hours.

A principal .objecttherefore of this invention is to eliminate a considerable part of this loss of time and to enable the ignition system to be quickly and conveniently tested so that faulty plugs can be located at once. Two essential requirements for accurately testing spark plugs for this type of service are that they be tested in the engine under normal operating conditions during which'they are subjected to the high temperatures and pressures of the engine cylinders, and also that the accuracy of testing be. not affected by interference by induction from nearby high tension conductors of. the ignition system.

A further object of this invention is to provide an improved method of and apparatus for testing spark plugs of multiple cylinder, dual-ignition internal combustion engines that does not require removal of the plugs vfrom the engine blockduring testing and that can be applied during normal operation oi the engine.

A further object of this invention is to provide improved means for preventing interference in the testing circuits by induced potentials from high tension conductors of other parts of the ignition System. a

A further object of this invention is to provide improved electronic means for giving accurate visual indication of the condition of a. spark plug under test.

A further object of this invention is to provide improved testing apparatus for spark plugs in dual-ignition, multiple cylinder internal combustion engines that is eilicient and simple in its arrangement so that it can be easily and rapidly applied and used for testing without a separate harness ordetector plug system, that neto by means of the dead or detector plugs of the inoperative magneto system. To this end, referring to a single cylinder, a potential is applied to a detector plug and electronic means associated therewith is controlled by the conductive condition of said plug during firing of the engine charge by the other twin plug for visually indicating when the live plug is firing.

The invention will be. more fully set forth in the following description referring to the accompanying drawings, and the features of novelty will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawings,

Fig. 1 diagrammatically illustrates the application of my invention to a dual-ignition multiple cylinder internal combustion engine;

Fig. 2 is a diagram of an electric circuit arrangement including electronic means for visually indicating testing results;

Figs. 3 and 4 are similar-diagrams showing modified forms of circuit arrangements for this purpose;

Fig. 5 is a similar view showing a modified form of circuit arrangement for increasing the duration of the visual indication;

Fig. 6 shows a further modified form of circuit arrangement for obtaining negative bias by means of a voltage regulator tube; and

Fig. 7 is an oscillogram illustrating the effect of discharge at the detector plug on grid bias potential.

Referring to Fig. 1 there is diagrammatically illustrated a. dual-ignition system of a multiple cylinder internal combustion engine of a type commonly used in aircraft. dual-ignition system includes two sets of spark pl'ugsso that each cylinder has two plugs, and a magneto connected to each-set of plugs so that As is well known, a-

the engine can be operated on either magneto if necessary. As illustrated, the No. l magneto and No. 1 and No. 2"magnetos respectively.

The No; 1 magneto and distributor is diagrammatically illustrated and since it may be of any suitable and conventional type a brief description will be sufficient. The magneto comprises essentiallya primary winding l5 that is controlled by the cam operated make-and-break contacts 16, and a secondary winding ll, one terminal ,of

which is grounded and the other terminal connected to the distributor arm l8. The distributor arm i8 and the m-ake-and-break cam 19 are operated by the engine in a wellknown manner so as to transmit the ignition voltage to the distributor contacts 20 for operation of the spark plugs. The cable ID for example whichincludes the conductors from the nine distributor points to the harness leading to the nine cylinders is provided with a Junction coupling 2! having an outlet receptacle 22 for each of the nine conductors. The cable l2 of the No. 2 magneto and distributor likewise is providedwith a junction coupling 23 having an outlet receptacle 24 for each of the nine conductors in cable i2.

In accordance with my invention the engine is run, while testing, on one ignition system only, such as'the No. 1 magneto and distributor and the No. 2 magneto is grounded by the switch 25 so that ignition to No. 2 system is dead. The inactive conductors of cable l2 are then connected to testing apparatus hereinafter described and indicated by way of example by the portable testing unit 26. The'unit 26 is provided with a flexible cable 21 having a plug connector 28 for connecting the contacts of the receptacle 24 to corresponding testing conductors of cable 21. As in the case of the cable l2 the cable 21 is shielded such as by means of metallic braid, for example,

and theplug and receptacle means 24-48 invenient source, such as a D. C. battery 29, or commercial A. C. power. There may be incorporated in the unit a vibrator, rectifier, dynamotor, or other suitable means for obtaining a D. C. supply for plate voltage and for ignition detection. The testing unit 26 is also provided with a plurality of indicating lamps 30, each lamp corresponding to a cylinder of the engine;

In brief; the testing of the spark plugs comprises alternately checking one set of plugs against the other during firing or burning of the engine charge. When flame strikes the detector plug, the ionization conductivity permits current to flow and the potential of the plug to drop.

This drop in potential is used to flash a neon lamp by means of an electron tube circuit, so that the lamp corresponding to a given cylinder flashes regularlywhen the active plug is in good 60 plug condition, and flashes intermittently or remains dark when the plug is faulty or badly fouled. After the plugs connected in No. 1 ignition system have been checked, the testing unit 2-6 is 5 disconnected from the cable l2, the engine is switched to the No. 2 ignition system and the No.

l ignition system is made dead by closing its 7 ground switch 25. The testing unit is then connected to cable lll through the receptacle 22.

The spark plugs of No. 1 ignition system now function as detector plugs for the spark plugs of No. 2 ignition, system.

Referring specifically to Fig. 2, which shows a one-plug testing circuit of the apparatus 26.

5 the input power terminals 3| and 32 are supplied with positive D. C. potential. Terminal 31, for example, is provided with a suitable voltage, such as 600 volts, and terminal 32 may be provided with 300 volts for the anode bias of electric valve means 33. The terminal 34 is connected to ground and the terminals 32 and 34 are interconnected by two series-connected resistances 35 and 35. An indicating lamp 37, such as a neon lamp. is connected between the terminal 34' and the junction 38 of the aforesaid resistances for dark, indicating that the tester cannot be properly operated. The lamp 31 also functions as a regulator by providing a steady positive bias for the triode valve V1. v

. The portion of the testing apparatus indi- 3 5 cated at A, Fig. 2, is common to the arrangement for testing all cylinders, whereas the part indicated at B is individual to each cylinder. Since but a single electron tube is required for testing each cylinder, the provision of a circuit for each 40 cylinder is' preferred, 1. e.. a tester for a nine cylinder engine would have nine electron tubes and nine indicating lampsas illustrated in Fig. 1. However it will be understood that a single test ing circuit used witha selector switch can also be employed to test each cylinder individually.

This could be used to advantage for flight testing since the unit would be small and of light weight.

When the testing apparatus is connected through the connectors 2428 to one of the spark plugs, such as plug I 4, for example, a D. C. potential from terminal 3! is impressed across that plug through the resistance 39. This potential also charges the condenser) through resistances 39 and 4!. Assuming that the plug l3 fires, causing burning of the combustion charge in the cylinder,

the flame at plug l 4 greatly reduces the di-electric strength of the gap, In this respect the plug i4 is similar to an ionization detector during propagation of flame. in the cylinder. When the gap or I4 becomes suiliciently conductive, the charged condenser 40 discharges through .the plug l4. This discharge in turn charges the condenser 42 in opposition to its normal, polarity of charge and thus reverses the normally positive potential of junction 43 that is connected .7 is-driven from a positive value to a much greater negative value. Reversal of the positive grid bias results in cut-' off of the valve V1 with the result that the voltage of the anode circuit 48 increases so as to apply 7 throughthe condenser 41 a positive signal to the control grid 48 of the triode valve V2 which is normally biased to cut-oil. This cut-oil? bias may i be automatically provided by the cathode emission of the valve V2 since the cathode of Va is electrically isolated when the lamp 30 is dark.

That is, a blocking charge canbuild up on the 85, such as a neon lamp corresp'onding to the lamps of the unit 28 in Fig. 1. This flash indicates that the plug it has fired the cylinder charge. The lamp circuit includes the anode circuit l9 and return-conductor 50.

After the voltage discharge through the detector plug H. the. grid potential of valve V1 the two plugs. the badly fouled plug would in.

this case fail to give satisfactory ignition, i. to fire the cylinder charge. Accordingly, both 'tests would point to trouble in a particular cylinder, and in such a case both plugs should be replaced.

My improved method of testing is not only ac-' curate but is very positive. It indicates definitely whether a cylinder is or is not firing, even if there is only occasional missing." The indication is simply the failure of the neon lamp to flash repeatedly so that an experienced operator is not required to interpret the lamp indications.

' The ignition trouble'is accordingly localized inrelaxes towards its quiescent positive bias as illustrated by Fig. 7 so that the valve again becomes conducting, causing a drop in its plate potential and a corresponding drop in potential, at grid 48 of valve Va. The valve V2 is accordingly made non-conducting until the next ignition flame is detected by'the plug i4. By providing suitable voltages at the terminals :1 and 32, even a weak detection signal can be relied upon to flash brightly the indicating lamp. 1

Since the high tension lead to detector plug I4 is located in the same'ignitlon harness with the active high tension leads of the No. 1 magneto, ignition interference may be picked up by the detector lead. This interference is reduced at the junction .43 to a negligible amount by means of the R. 0. filter or integrator circuit defined by the resistance 4i and the condenser 52, so that it does not materially affect the grid bias of valve V1.

The capacitance to ground of the leads between the testing apparatus and the engine may also act asa capacitance divider to reduce the strength of the ignition interference. Sufllcient positive bias of the valve V1 prevents accidental interference from triggering the circuit. Unless the individual leads are separately shielded in the connector cable 21, the mutual capacitance between leads may dissipate the strength of the desired ignal and induce a signal which may cause the other channels to be triggered accidentally. The use of individually shielded leads in the flexible cable 21 is therefore preferred.

In certain cases, it may be desirable because of interference difiiculties to introduce a slight time delay in the flashing of lamp 30. This can be accomplished by connecting a condenser in parallel with the resistance 52 of the plate circuit of valve V1. When the cut-oil of valve V1 takes place, its plate potential rises at a rate determined by the R. C. combination described; This rate can be chosen to introduce a. certain time delay that is effective to eliminate interference peaks which otherwise might have gotten tector plug should be replaced. Also when the test is repeated with interchange of function of the particular circuit which falls to fire the cylin der charge and in most cases the trouble can be cleared by replacement of the spark plug. If after such replacement trouble still exists vin this particular circuit, a standard harness and magneto tester may be used to locate the trouble in this circuit.

As a matter of convenience the testing apparatus may be provided with a so called "memory switch ii that is closed if the lamp 30 indicates faulty ignition. Closing of the switch 5| completes the circuit of the lamp 30 so that it remains lighted after the ignition testing is completed. The memory switch 5| can conveniently be-a small toggle switch positioned if desired beside the corresponding indicating lamp.

I have provided alternative arrangements for I controlling the electronic means for flashing the indicating lamp in view of the fact that operating conditions may require different circuit characteristics. In the arrangement shown for example in Fig. 3 the cut-off bias of the valve V2 is obtained by means of the resistance 53. When the resistance 53 is carrying a bleeder current and the normal plate currents of the valve V1 it biases the cathode of the valve V2 sufficiently positive to hold the valve at cut-off. In other respects the circuit is essentially the same as that of Fig. 2, the indicating lamp 30 being connected in the load circuit of V2 by conductor 54 so as to flash when valve V2 is conducting, and the power indicating and regulating lamp 37 functioning as in the case of Fig. 2.

Fig. 4 illustrates a basically similar circuit except that in this case the cut-off bias of the valve V2 is obtained'by means of a resistance 55. This resistance when carrying. the normal load or plate current of the valve V1 biases the cathode of the valve V2 sufficiently positive to maintain the valve at' cut-off. By means of resistance 55 I also provide for equalizing the brightness of all flashes of lamp 30 by utilizing the principle of re- .generation. The cathode of valve V1 is biased.

power supply from being introduced between the I 1 cathode and grid of V1.

The lamps 30 and 31 both function in the manner above described.

In certain cases an unusual amount of interference may be encountered. Since a high posi tive bias is desirable at the punction 43 to prevent interference from triggering the circuit, and since low positive bias is desirable so that even weak ignition detection signals can trigger the circuit, I provide means for automatically reducing the positive bias when the cylinder is firing. To this end the Junction points X and. Y may be interconnected by a resistance and condenser in parallel as indicated by Fig. 4. When voltage to reduce the positive bias at V1. p the caseof Fig. 4 the "burning voltage" of lamp so applied in the case of Fig. 2, the neon lamp I w 30 provides a higher than normal voltage so as to develop an increased voltage across the R. C.

circuit between X and Y. I V l Fig. 5 shows an arrangement operable at stated a positive potential at the'cathode oi the tube V1. This regenerative feature increases the duration of the flash of lamp 3!] and also makes the duration of the flash substantially the same for any irregularity of signal from the detector plug. Thus the brilliance of the flash is increased and made uniform. After the discharge through the plug it the grid-potential of valve V1 increases to a value higher than its quiescent bias since the resistances 58 and N do not act as voltage divider while V1 is non-conducting. The valve V1 becomes conducting when its grid rises sufllciently positive to cancel the voltage drop of the lamp current flowing in resistance I1. Thus the relaxation of the V1 grid bias from a large negative signal to a high positive value permits a long and uniform ilash from the lamp 30.

After relaxation or junction 43 from the large negative signal, valve V1 again is made conducting. The saturation value of plate current causes a large decrease of plate potential which impresses a large'negatlve signal on the grid valve.

Va. This signal in conjunction with the normal negative bias extinguishes the lamp 30 and holds it non-conducting until the next flame is detected by the plug, ll. Likewise during this interim, normal positive quiescent bias of valve V1 is obtained as the excess positive potential of Junetion I relaxes by virtue of condenser 42 discharging through flow of grid current in valve V1.

In thecircuit of Fig. 5 a D. C. battery I! is used for providing the normal negative" cut-oi! bias for the valve V2. It will be noted that the high potential terminal II used in the previous circuits is not included. For this reason the circuit of Fig. 5 can use the regenerative feature to particular advantage since weak detection sig nals might otherwise fail to produce a suiilciently brilliant indication.

Fig. 6 illustrates a further arrangement for obtaining cut-oi'f bias of the valve V2. A gas filled voltage regulator tube 60 is in this case connected directly from ground to the cathode of the valve-Va. Although in this case the detector lamp current fiows through tube 80, the steady voltage bias required is provided by the constant voltage characteristic of the tube.

It will therefore be seen that my invention provides for quick location of a faulty plug circuit so that the removal and replacement of all engine plugs can be avoided, thereby reducing to a large extent station. delays due to ignition troubie which is at present responsible for more than half of the station delays.

It should be'understood that this invention is more spirit of the invention; For example, although I have shown my invention in its application to a high-tension ignition system, it should be understood that it can alsobe applied to any ignition system by making suitable connection to a detector plug within the combustion chamber.

I claim:

1. The method of testing the spark plugs of a dual-ignition, multiple cylinder internal combustion engine-while in operation which comprises running the engine on the first ignition system only, applying a testing potential tothe spark plugs of the second ignition system for detecting I faulty plugs in said first system. running the engine on said second ignition system only and applying a testing potential to the sparkv plugs of said first ignition system for detecting faulty plugs in said second system. a

2. The method of testing the spark plugs of a dual-ignition, multiple cylinder internal combustion engine while in operation which comprises running the engine on the first ignition system only, applying a testing potential to the inactive spark plugs of the second ignition system for checking the plugs of said first system by determining the conducting condition ofthe engine charge, running the engine on said second ignition system only and applying a testing potential to the inactive spark plugs of said first ignition system for checking the plugs of said second system by determining the conducting condition of the engine charge.

'3. The method of testing the spark plugs of a dual-ignition, multiple cylinder internal combustion engine while in operation which comprises running the engine on the first ignition system only and applying a testing potential to the inactivespark plugs of the second'ignition system, said no ential being sufilcient to cause voltage breakown of the spark plug gaps only during firing of the engine charge, detecting voltage break-down at said gaps, running the engine on-said second ignition system only and applying a similar testing potential to the inactive spark plugs of said first ignition system the inactive spark plugs of the second ignition not limited to specific details of construction and arrangement thereof herein illustrated, and that system for causing breakdown at the gaps of said plugs during normal firing oi the engine charge, detecting for visual indication said normal firing evidenced by breakdown at the respective gaps, running the engine on said second 'ignition system only and applying a testing potential to the inactive spark plugs of said first ignition system for causing breakdown at the gaps of said plugs during normal firing oi the engine charge, and detecting for visual indication said normal firing evidenced by breakdown at the respective gaps.

5. Testing apparatus for a dual-ignition, internal combustion engine adapted to run on either ignition system while the other ignitionsystem is dead comprising means for selectively connecting said apparatus to a dead ignition system of said engine, means for impressing a potential on a spark plug in the dead ignition system so as to cause breakdown at the gap of said plug during normal firing of the engine charge by the twin plugof said other ignition system, electronic means associated with the dead plug and responsive to potential variation caused by the gap breakdown at said plug, and means controlled 6. Testing apparatus for a dual-ignition, mul- I tiple cylinder intemal combustion engine adapted lectively connecting said apparatus to a dead ignition system oi said engine, meansior impressing a potential on a spark plug in the dead ignition system so as to cause discharge through said plug during normalfiring oi the engine chargeby the twin plug of said other ignition system. a control circuit including electronic valve means responsive to potential variation caused by discharge oi said plug, and an indicating lamp controlled by said electronic means and-arranged to be flashed when said engine charge is fired.

7. Testing apparatus for spark plugs of a multiple cylinder internal combustion engine having two spark plugs for each cylinder and a magneto for each set oi. said plugs, arranged so that the engine can be run on either magneto while the other magneto is dead comprising means for applying a testing potential to each of the plugs connected to the dead magneto, electronic means responsive to the conductive condition of each of saidplugs during normal firing of the engine charges by the operating magneto plugs, and means controlled by said electronic means for indicating said normal firing.

,8. Testing apparatus for spark plugs of a multiple cylinder internal combustion engine having two spark plugs for each cylinder and a magneto for each set of plugs, arranged so that the by said electronic means for indicating said breakdown.

on a spark plug of the corresponding cylinder in the dead ignition system so as to cause discharge through said plug-dur'ing normal firing oi .the engine-charge by the twin plug of said other ignition system, valve biasing means responsive to said discharge, an electronic valve normally biased to cut-oi! and controlled by said biasing means so as to be conducting during said discharge. and a lamp gperatively connected to enginecan be run on either magneto while the f other magneto is dead comprising a direct current source, a condenser arranged to be charged from said source for applying a testing potential to a plug connected to the dead magneto, said said valveior indicatingsaid discharge and normal firing. 4 7

a 11. Testing apparatus for spark. plugs oi an internal combustion engine having a detector in the cylinder of the plug being'tested, comprising a control'circuit including a condenser for applying a testing potential to said detector, an electron valve having a control grid, means controlled by the conductive condition oi! said detector during the condenser; discharge incident to normal firing of the engine charge for increasing theg'rid potential of said valve so that it becomes conducting, and a lamp controlled by said electron valve for indicating said normal firing. l

12. Testing apparatus for detecting a sudden increase in conductivity ,of a circuit comprising a condenser arrangedto be charged by a D. C. potential, means connecting said condenser to said circuit so that 'the condenser discharges through said circuit in accordance with a sudden predetermined increase in conductivity of said circuit, an electron valve having a control grid,

. means responsive to potential variation incident to discharge of saidcondenser for increasing the control potential of said-valve so that it becomes conducting, and an electron lamp for indicating the aforesaid increases in conductivity when said I valve becomes conducting, said lamp being concondenser arranged to discharge through said i plug during normal firing of the engine charge by the operating magneto plug, electronic means responsive to the potential drop caused by said condenser discharge, and means controlled by i multiple cylinder internal combustion engine having two spark plugs for each cylinder and a magneto for each set of plugs, arranged so that the engine can be run on either magneto while the other magneto is dead comprising meansior applying a testing potential to a plug connected to the dead magneto so as to cause current flow through said plug during normal firing of the engine charge by the operating magneto plug, an electronic valve arranged to be biased to cut-off in response to said current flow, a second electronic valve normally biased to cut-off and controlled by said first valve so as to be conducting when said first valve is non-conducting, and means controlled by said second valve for indicating said normal firing.

10. Testing apparatus for a dual-ignition multiple cylinder internal combustion engine adapted to run on either ignition system whilethe other ignition system is dead comprising a portable unit that can be selectively connected to a dead ignition system of said engine, said unit having a source of .D. C. potential and comprising a testing circuit for each cylinder of said engine, each circuit having a condenser arranged to be charged by said potential so as to be impressed 75 adapted tobe selectively connected to a dead ig-,

responding plug of the operating system, and,

nected in the cathode circuit of said valve so as normally to isolate said cathode and to cause an increase in cathode potential due to cathode emissionior normally biasing said valve to cut-off.

13. Control apparatus comprising a circuit including a pair of electron valves each having a control grid, said valves being arranged so that biasing of the first valve to cut-off causes the second valve to become conductive, an electron lamp in the load circuitof said second valve for indicating conduction of said valve, and a parallel connected resistance and condenser electrically connected to the control grid of said first valve and arranged to be charged by said electron lamp whereby thepotential on said control grid is lowered duringa rapidly recurring cycle of opera tion of said valves and is permitted to increase when said valves are quiescent to prevent accidental cut-off of said first valve and triggering 0 said circuit by interference.

14. Testing apparatus for the spark plugs of a dual-ignition internal combustion engine adapted to run on either ignition system comprising means means controlled by said current flow for indicatnitionsystem while the other system is op rating i'or impressing the condenser charge on a spark plug of the dead system, said charge causingwiiow l of current through the spark gap'at said plug when the cylinder charge is normally tired by the corresponding plug'ot the operating system, and

electronic valve means controlled by said current flow for indicatins said normal tiring.

16. A sparkplug tester for indicating normal firing under load conditions within an internal combustion engine comprising means apart from the plug to be tested for detecting ionized combustion gases incident to iirins otthe cylinder charge by said 'plug, and an indicating device, said detecting means including electronic valve means for controllingsaid indicating device." j

WILLIAM MALCOLM BAUER.

REFERENCES cI'rEn The following references are of record in the iile of this patent:

UNITED STATES PATENTS Schade "Nov. 12, 1946' 

